1. Field of the Invention
The present invention relates to a method for forming a multi-layer interconnection of a semiconductor device, and more particularly relates to a method for forming micro-size contact holes for the electrical connection between lower and upper interconnection layers fitted with the fabrication of highly integrated semiconductor devices.
2. Description of the Prior Art
Generally, a semiconductor device is fabricated in the multi-layer interconnection structure. In this multi-layer interconnection structure, a lower interconnection layer and an upper interconnection layer are electrically isolated by an insulating layer having a contact hole, and are electrically connected through the contact hole to each other.
The conventional method for forming the multi-layer interconnection structure will now be described. First, there is provided a semiconductor substrate on which a lower interconnection layer covered by an insulating film is formed. The lower interconnection layer is a metal interconnection or an impurity diffusion region. A contact mask such as a photoresist pattern is then formed on the insulating film. By etching the exposed portion of the insulating film, a contact hole is formed in the insulating film in such a manner that the lower interconnection layer is partially exposed. In the contact hole, there is a contact layer formed in such a manner that it is in contact with the lower interconnection layer. Then, an upper interconnection layer is formed on the insulating film in such a manner that it is in contact with the contact layer.
The contact hole and the contact layer may be formed by a damascene process. In this damascene process, the contact hole is first defined in the insulating layer. A conductive layer is deposited on the insulating film in such a manner that it buries the contact hole. Then, the portion of the conductive layer protruded from the insulating film is removed, thereby forming the contact layer.
In the forming method of the multi-layer interconnection as described above, the contact hole is formed through masking and etching processes. In this case, a realizable size of the contact hole is dependent on a resolution of an exposing system. Namely, the size of the contact hole is limited by an aperture pattern formed on a contact mask, and the size of the aperture pattern formed on the contact mask is dependent on the resolution of the exposing system. For this reason, the realizable size of the contact hole is dependent on the resolution of the exposing system.
A certain size of the contact hole can be realized by the use of an existing exposing system. However, a contact hole having a more reduced size, that is, a micro-size contact hole capable of being fitted with a future tendency toward a high integration density and a design rule reduction, will be not defined, unless a new exposing system is provided.